“Time flies like an arrow. Fruit flies like a banana.”

Time travel is easy, explaining it is hard.

I was looking over my time travel rules (posted here). I was thinking that I hadn’t explained them very well and that I also needed to re-work them for the next version of D&D. The more I thought about it, the more I realized that they needed a complete overhaul. Before posting a new set of time travel rules I wanted to post this. Below is a summary of my current thinking on how time travel should work for D&D.

First a little thought experiment

Consider this. Your friend the wizard travels 24 hours into the past. While there, he sneaks into your room and shaves your head while you sleep. The question is this: If you are watching him when he cast the spell and he disappears into the past, what do you experience? Are you now bald? There are problems with every answer.

1) You can’t still have your hair. If you do it would mean that the wizard was unsuccessful in changing the past.

2) You couldn’t just suddenly become bald. What if the wizard doesn’t cast another spell to “return” to the present, but simply hangs out with you all day?

3) Okay, then perhaps your head is shaved, and it has been since you woke up this morning. This is a paradox, because if you have been bald all day it would mean that you were that way before the wizard cast the spell that resulted in your current condition.

There must be another answer, and I believe that I have found it. Think about this a little. I will give you the answer a little later.

This is how I think time travel should work in the D&D game.

Timelines

There is only one timeline. Everyone is in it. The “river of time”. It is easy to travel forward in time. Everyone does it. You are doing it now. It takes only one second to move forward one second into the future. If you were to sleep for 17 years, you would wake up 17 years in the future.

All time travel is along this one timeline. Although there is only one timeline, this doesn’t mean that it can’t be changed.

Rule #1 – “Everything that you do changes the future.”

This may seem so obvious that it is hardly worth mentioning. However remember that we are talking about time travel. If you travel along the timeline to a point in the past anything you do there will change everything on the timeline from that point forward.

Rule #2 – “You can’t change the past.”

Well, I suppose you could travel to the past and then change it, but nothing that you do now can change anything that was done before. Again, this seems obvious but it is worth remembering that you can’t travel into the future and do anything that will change what is happening in the present.

There are two types of time travel, tactical and strategic.

Tactical Time Travel

Similar to time travel in the movie “Groundhog Day”.

Tactical time travel is free from most time travel paradoxes. It moves the timeline forward or back to the appointed time. It is not normally used to travel farther than a single day and cannot be used to travel back to a time before the time traveler was fully grown. Tactical time travel has no “return” spell that allows the traveler to go back to his original time, but he can use strategic time travel to go back should he choose to.

Tactical Time Travel to the Future

In its simplest form, this is how everyone travels through time, one second at a time. For a time traveler that uses tactical time travel to go into the future the time passes so quickly that he seems to instantly appear at the appointed time in the future. To those around him, he disappears and later re-appears. The timeline has moved on and he has moved with it as if he had been in a type of suspended animation during the time that passed. This is often used to “hide” from an otherwise unavoidable encounter or to disappear until the storm passes.

Tactical Time Travel to the Past

This is often used to correct some mistake in the recent past, or to re-fight a recent battle. The timeline is erased back to the time traveled to. It is like pressing the “rewind” button. Everyone and everything reverts to the way it was then. The time traveler finds himself in the body he had then, where it was then, doing what he was doing then, and everything is as it was then with the exception that the time traveler, and he alone, recalls future events as they happened before. He is free to repeat his previous actions or change them as he sees fit. Everyone else will do what they did before unless the time traveler intervenes. Purely random events may have different outcomes. All dice will be re-rolled for any battle or game of chance that the time traveler participates in.

The time traveler cannot magically “return” to the time he left because that timeline has been completely erased. If he does use a strategic time travel spell to travel forward again, he disappears and doesn’t re-appear until he reaches the time he is traveling to. No time will have passed for him but to everyone else, time will have passed normally until he re-appears. This effectively erases him form the timeline for that period of time. The time traveler that travels into the past using tactical time travel will typically continue through time at the normal pace making whatever changes to his previous actions as he chooses. When he arrives at the point in time where he originally chose to travel into the past, he is free to do so if he wishes. The reason for him to travel back in time may no longer exist, so he may choose to not repeat his trip to the past.

Strategic Time Travel

Similar to the time travel in the movie “Back to the Future”.

Unlike tactical time travel, strategic time travel is susceptible to time travel paradoxes so care should be taken to prevent them. Refer to the section below on time travel paradoxes.

Strategic time travel allows travel both forward and back in time to any point in the past or future.

With strategic time travel, the traveler appears at the appointed time in the past or future, and his original body disappears – usually to return in a few seconds when the traveler returns from his journey. The time traveler arrives at the prescribed time with a duplicate of his body and everything he was wearing or carrying. Any time while on his journey, he can cast a spell to “return” to the time he left. When he returns his body is in the condition it was in at the end of his journey and he will bring back with him whatever he is wearing and carrying.

If, at any time during his journey, he is knocked unconscious or killed he will return to his original timeline and his body will re-appear and collapse to the floor still wearing and carrying only what he had when he left. Everyone at the time that he traveled to will see him collapse. His body and everything that he was wearing or carrying when he began his journey will disappear, leaving behind anything he may have picked up while he was there.

Strategic Travel to the Future

The time traveler appears at the appointed time in the future, and at the same location as when the spell was cast. The future that he finds is the most likely future based on how events were progressing when he left. The time traveler himself disappeared when the spell was cast and has not been there to effect changes. If he travels to the same time in the future more than once, each time he will find the future somewhat different. He cannot meet with himself in the future because each trip forward is to a different future that did not have him in it.

Strategic Travel to the Past

The time traveler appears in the past but he has not moved from where he was standing when the spell was cast. Using strategic time travel, it is possible for the time traveler to encounter himself. It should be fairly easy to avoid such encounters and avoiding them should be encouraged. Strategic time travel spells can be used to travel to times before the time traveler was born.

When the traveler cast the “return” spell to go back to the time he had left, things may not be as they were when he left. If he traveled far into the past, before he was born, things that he did then will affect the way things are now. For example, if he killed someone in the past, not only will that person no longer exist, but everything that that person did after he killed him will never have happened. This includes any children that that person may have had after that point, they were never born.

Back to the thought experiment

The problem with the thought experiment I presented above is in the question. It assumes that you will still be there after the spell is cast.

The answer depends on whether the wizard used a tactical or strategic time travel spell (as described above).

If it was a tactical spell, not only would the wizard disappear, but you and everyone else would also. The timeline will have been erased back to a point in time that existed 24 hours earlier. You will have no memory of anything that happened in the last 24 hours, which is now in your future. Everything will progress from there and when you wake in the morning you will be bald. When it comes around to the time where he originally cast the spell, he will have no reason to cast it this time.

If the spell that the wizard cast was a strategic spell you would see him disappear and would notice nothing else unusual until he re-appears a few seconds later. When he re-appears you will at that instant be bald. You still won’t notice anything else unusual because you won’t feel that you suddenly become bald. When you woke up this morning someone had shaved your head while you slept.

Time Travel Paradoxes

The Grandfather paradox

So… You may ask, “What if I were to accidently kill my Father or Grandfather?”

To answer this we must first examine the role of the soul in D&D.

When a player character travels in time, his is moving with his soul to a different point on the time line.

All sentient beings, including all player characters, have a soul. In earlier versions of D&D elves did not have souls, but that was changed in more recent versions of the game. Each soul experiences time in an uninterrupted string of events, starting when the soul is created and ending when, or if, it is destroyed.

In Dungeons and Dragons, all souls in the multiverse originate from fonts on the positive energy plain. When a sentient being is born, his soul enters his body with his first breath. How long that soul existed before it occupied the newborn and how the choice of host is made is not known. A PC’s soul then continues throughout his life and beyond. A PC’s soul isn’t typically destroyed when he dies and if he is brought back to life, his soul re-joins his body. It is possible for his soul to be moved into an object or another body or travel to other planes. In a very real sense, a player’s character is his soul. Everything about him can change, but his soul remains and it existed before his body did. If his newborn body wasn’t available for his soul to inhabit because he was prevented from being born for any reason, his soul would have gone into another body. This body would have been as close to the same as possible. In order of preference the chosen newborn would have the; same Mother, same Father, same family or close relative, same neighborhood and similar family.

This means that you can’t really prevent yourself (meaning your soul) from being born. At the worst you will have been raised in a different family. Regardless of which newborn your soul first inhabited you would now still be the same sex and race. Your physical appearance would be nearly identical and all of your abilities would not change.

The Butterfly Effect

“What if I do something like, say, accidentally stepping on a bug in the past? Couldn’t that possible cause great changes in the future?”

Well, that is one theory. Just like the way that a butterfly flapping its wings in Brazil can affect a weather system in Texas, one tiny change in the past can lead to all kinds of Rube Goldbergian complications that can subtly — or seriously — affect the present. However, that would put a serious damper on the fun of doing things in the past. Time travel in D&D must be more forgiving that that. So let’s say this; “The river of time is hard to change.”

Time flows forward as a viscous, syrupy thick river that is quiet difficult to change in any meaningful way. Although small day-to-day changes are easy to make, the course of history is such a wide and powerful force that actions taken by individuals have little effect on future history. As this relates to time travel, you can forget about the “butterfly effect”. Minor changes in the past have no effect on the present. Even large changes have only a small chance of affecting the present. The farther you travel into the past, the less likely it is that anything you do will have any effect on the present.

All major events in the past would have still happened even if the person (or creature) that caused that event was killed. Another would have done almost the same thing. Perhaps it would have been done at a slightly later date, or in a different way, but it would have still happened. The existing opportunity and situations will result in someone else filling the void left when the original perpetrator was not there.

This doesn’t mean that you can’t effect the present by changing the past. Otherwise why bother with time travel? It is just that the changes you make must be deliberate and specific to have much effect on the present.

All Other Paradoxes

“Are you trying to tell me that there is no danger of creating a time paradox? What If I caused my past self to be killed? What if something travels from the future to the past, and becomes the item that was sent back in time in the first place, thus, having no discernible origin, creating an infinite loop? I can think of a dozen other potential ‘impossible’ situations that could be caused by time travel. What about those?”

The potential for creating paradoxes is quite high. Part of the fun for players and DMs alike is how the PCs handle this potential danger. What I am attempting to do here is help the players by providing a consistent set of rules and to help the DM by providing a logical overview of how time travel works so he can apply his understanding of the concepts involved when dealing with all of the unexpected things that the PCs may do. Rather than saying that there can be no paradoxes it is my opinion that the DM should make accidental paradoxes unlikely by handling the Grandfather paradox and any Butterfly Effect paradoxes as indicated above. The DM can also provide the players with an easy way to avoid paradoxes. He should remind the players that there is no reason for you to interact with your previous self if you choose not to. This simple precaution should avoid most potential paradoxes.

How to Handle a Paradox

Regardless of precautions the PCs may end up creating a paradox. The best way to handle this is to assume that the timeline is self-correcting. Any paradox will cause the destruction of the part of the time and space affected by the paradox.

So, if a PC travels back and kills his former self, then it will cause himself to disappear. History will erase all traces of the person’s existence, and the death of the PC will have been caused by another reason. Thus, the paradox will have never have occurred from the historical viewpoint.

So now what?

I intend to create a set of rules compatible with D&D Next using the ideas presented above. If you have any questions or comments please let me know. As I said, explaining time travel is hard.